Carbon Cycle Flashcards
Photosynthesis
transfers atmospheric carbon into biomass. Plants and phytoplankton use energy from the sun to change carbon dioxide and water into glucose and oxygen - enabling plants to grown. Carbon is then passed through the food chain and released through respiration and decomposition.
Combustion
transfers carbon stored in living dead or decomposed biomass to the atmosphere by burning. The organic material can be any vegetation or fossil fuel (e.g. natural gas, oil or coal). Organic materials contain carbon and hydrogen; sometimes oxygen too. Any other elements present combine with oxygen to from a variety of pollutant molecules, such as sulphur oxides and nitrogen oxides.
Respiration
respiration transfers carbon from living organisms to the atmosphere (photosynthesis and respiration are essentially the opposite of one-another). Plants and animals break down glucose for energy, releasing carbon dioxide and methane in the process.
Decomposition
Decomposition transfers carbon from dead biomass to the atmosphere and the soil. After death, bacteria and fungi break the organism down. CO2 and methane are released. Some carbon is transferred to the soil in the form of humus. Decomposition ensures that the important elements of life (carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur & magnesium) can be continually recycled into the soil and made available for life.
Weathering
Chemical weathering transfers carbon from the atmosphere to the hydrosphere and biosphere. Atmospheric carbon reacts with water vapour to form carbonic acid (acid rain). When this acid rain falls onto calcium carbonate rocks (e.g. limestone), a chemical reaction occurs which creates a weaker rock (calcium bocarbonate). This is easily dissolved by running water. Carbon molecules resulting from this reaction may be washed into the sea, where they react with CO2 dissolved in the water to form calcium carbonate which is used by sea creatures to make shells (e.g coccoliths).
Sequestration
Carbon from the atmosphere can be sequestered (captured and held) in sedimentary rocks or as fossil fuels. For example, following on from the weathering process described earlier, when coccoliths die, they fall to the ocean floor to create carbon-rich sediments which form carbonate rocks over time (e.g. limestone).
Fossil fuels also form over millions of years when dead animal and plant materials in the oceans falls to the floor and are compacted. Carbon in fossil fuels is sequestered until we combust them
Ocean uptake and loss
CO2 is directly dissolved from the atmosphere into the ocean. Warm tropical water (carried to cold polar regions by ocean currents) is cooled and sinks (due to increased density) to the ocean floor - transferring carbon dioxide to deep ocean water. This is then released to the atmosphere near the tropics - carbon-rich water rises to the surface and releases CO2. This is known as the oceanic pump.
Carbon is also transferred to the oceans when it is taken in by organisms that live in euphotic zone near the ocean surface (e.g. phytolankton). These organisms photosynthesise and are then consumed as part of the food chain. The carbon is then incorporated into marine organisms as organic matter or structural calcium carbonate. When the organisms die, their dead cells sink into deep water, forming layers of carbon-rich sediments which turn into sedimentary rock (locking up carbon for millions of years). This is known as the biological pump.
Atmosphere carbon store
- levels have fluctuated during earth’s history
- due to human activities, the present levels are higher than they have been in the last 800,000 years.
- plays a huge part in global temperatures
Cryosphere Carbon store
- less than 0.001% of earth’s carbon
- found in permafrost (permanently frozen for at least 2 years)
What is a positive feedback loop?
When a change to the input amplifies the output.
What is a negative feedback loop?
When a change to the input nullifies the output.
Positive feedback in the carbon cycle
Wildfires release large quantities of co2 into the atmosphere through burning, this co2 enhances the greenhouse effect, the greenhouse effect causes more wildfires, as it creates hotter and drier climates.
Negative feedback in the carbon cycle
Global warming is enhanced by co2 emissions. Higher temperatures and higher levels of co2 increases photosynthesis rate and creates new areas of vegetation, so co2 is taken in by plants through photosynthesis, less co2 is now in the atmosphere so it reduced the global warming effect so photosynthesis returns to post-warming levels (no longer accelerated by co2 and global warming)
